Isotope separator



Aug. 17, 1954 w. E. GLENN, JR

ISOTOPE SEPARATOR Filed OCT.. 23, 1951 Q5.. Y Q5 m6 vm Y V o o GTJNVENTOR. W/LL/AM E. GLS/VM JR Afro/wax Patented Aug. 17, `1954 WilliamE. Glenn,

Jr., Berkeley, Calif., assignor to the United States of America asrepresented by the United States Atomic Energy Commission ApplicationOctober 23, 1951, Serial No. 252,755

6 Claims.`

lThis invention relates to an isotope separator` and more particularlyto an apparatus for separating ions according to their respectivemasses.

The art of mass spectrometry has been greatly developed during recentyears; however, the apparatus which has been designed heretofore, has

required the use of a magnetic field, complex control circuits, andintricate detecting equipment resulting in bulky and difcult-to-handleinstallations. These types of mass spectographs have been based on thetheory that ions projected through a magnetic field are forced intocurved paths according to their mass. Thus, with detecting equipmentappropriately disposed along the ion paths, it is possible to determinethe presence of ions of different masses in a test material. The presentinvention allows the determination of the mass of the ions present in atest material without the use of magnetic field and with a minimum ofeffort on the operators part. The present invention lends itself to massproduction methods of manufacture and because of its simplicity can bemade at a very reasonable cost.

It is therefore an object of this invention to provide a new andimproved isotope separator.

Another object of the present invention is to provide a linear isotopeseparator wherein a magnetic structure is not necessary.

Still another object of this invention is to provide an apparatus ofextreme sensitivity for determining the mass numbers of ions.

A still further object of this invention isto provide a method ofseparating and recovering a plurality of isotopes in small quantities.

Another object of the present invention is to` provide a compact andeasily manufactured isotope separator characterized by its simplicity ofoperation.

Other objects and advantages will be apparent inthe followingdescription and claims considered together with the accompanying drawingwhich shows a sectional view of the isotope separator and its associatedelectronic equipment.

Referring to the drawing in detail, there is shown an envelope IIdefining a vacuum charnber I2 therein. One end of the envelope il isopen and formed with an outwardly extending flange I3. A centrallyapertured cover plate I4, made of an insulating material such as hardrubber, has a plurality of holes I6 drilled to match a similar number ofholes I'I drilled and tapped in the ilange i 3. Thus the cover plate I 4can be secured to the flange I3 by bolts I8. To provide an airtightconnection between the cover plate and flange, a rubber gasket I9 isfitted in a groove provided in the face of the flange I3. l As a meansof evacuating the chamber IZ. the envelope II is provided with anexhaust outlet 22 communicating with a conventional vacuum pump23. i

i ing a photographic lin 5B .l ameter of the cylinder 5I Mountedcentrally on the inner surface of the cover plate is a `rst copper tubesection 2li having substantially the same diameter as the centralaperture in the cover plate lli and having a flange Z5 bolted to thecover plate with bolts 21. A series of tube sections 28, similar to theiirst section 24 without the ii'ange 26, are mounted in 4axial alignmentand in spaced-apart relation by means of two or more resistors 2Ssoldered between each successive pair of tube sections. The resistors 29mounted in such a manner serve to support the series of tube sections 23as a unit and also to distribute a voltage across the gaps formed, aswill be explained more fully hereinafter. iThe series of tube sections28 is terminated in a tube section 3l, which is similar to the rst tubesection 2li, and having a flange 32. Attached to the flange 32 by nalboard34 made of an insulating material such as that used for the coverplate ill. A ribbonlike filament 36 of a material such as tungsten ornickel-chromium alloy is mounted on pillars 3l which in turn arefastened to the terminal board 34 by bolts 33 in such a manner that thefilament 3G is centrally located Within the tube section 3l Extendingacross the open end of the tube section Slis a screen-type gridstructure 39. A similar grid structure is mounted across the opposingend of the adjacent tube section 28.

Acylindrical tube ft2 made of insulating material and having the sameinner diameter as the central aperture of the cover pla-te I4, is formedon the cover plate on the side opposite the copper tube section 2li.Extending across the cylindrical tube 42 is a screen-type grid structureIM similar to the grid structure 33. An electrical connection 46 extendsfrom the grid structure 4d to theexterior of the cylindrical tube 32. Aslmilar grid structure di spaced apart along the longtudinal axis of thecylindrical tube l2 extends thereacross. An electrical connection iidextends from the grid structure il to the exterior of the cylindricaltube d2. A wide fiange dit having substantially twice the diameter ofthe cylindrical tube 42 extends outwardly from the second end of thecylindrical tube. A metallic cylinder 5i which, in the preferredembodiment, has an inside diameter substantially twice that of theinside diameter oi the cylindrical tube l2 and has one end thereoffastened by means of an outwardly extending flange 52 and bolts 53 tothe Wide flange 59. The other end oi the metallic cylinder 5I has anoutward iiange 54 which is fastened by means of bolts 56 to a coverplate 5l made of insulating material. Means for retainon the interiorsurface of the cylinder 5I comprising spring clips 5S is provided.Axially disposed within the cylinder 5I is a metallic rod iii which, inthe preferred embodiment, has a diameter at least 0.1 the diand which issupported bolts 33 is a termiat one end by a machine screw 62 extendingthrough the cover plate 51.

The accompanying electr prises a iilament voltage supply 63, anaccelerating voltage 64, a saw-tooth voltage supply 66. a unidirectionalvoltage supply |51, and a triggering circuit 53, all of which areconventional electronic components. The lament voltage supply has twoterminals IIiI and |02. The terminal IBI is connected by a wire |03 to aterminal |24 on the external face of the cover plate I4. Internally theterminal |04 is connected by a lead |06 to a terminal |01 on the board34 which is in turn connected by a wire |38 to one of the bolts 38 andthus to one side of the filament 35. The terminal |62 is connected by alead I II to a terminal H2 on the cover plate I4 which is internallyconnected by a wire |i3 to a terminal I I4 on the board 34. The terminalI I4 is further connected by a lead H5 to the other bolt 33 which iselectrically connected to the other side of the lament 36. Thus it isseen that the voltage of the iilarnent power supply t3 is connectedacross the lament 35.

The accelerating voltage supply 54 has two terminals i2| and `522. Theterminal I2| is connected by a lead |23 to a terminal |24 on the coverplate I4 which is internally connected by a wire |25 to a terminal |21on the board 34. The terminal |21 is in turn connected electrically by aconductor |28 to one of the bolts 33. The terminal |22 is connected by awire |3I to a terminal |32 on the cover plate I4 and the terminal |32 isin turn connected by a lead |33 to the iiange 25 of the rst tube section24. Therefore the accelerating voltage between the terminals |2| and |22of the accelerating voltage supply 64 is impressed across the series oftube sections 24, 28, and 3|.

The saw-tooth voltage supply 56 has two output terminals I4| and |42.The terminal I4I is connected by a lead |43 to the electrical connection4G of the grid structure 44 in the cylindrical tube 42. The terminal |42is connected by a lead |44 to the electrical connection I3 of the gridstructure 41. Thus the saw-tooth voltage is applied across the two grids44 and 41 in the cylindrical tubev 42.

The unidirectional voltage supply 61 has two output terminals I5| and|52. The terminal |5I is connected by a lead |53 62 in the center of thecover plate 51, which is electrically connected to the metallic rod 3 IThe terminal |52 is connected through a lead |54 to one of the bolts 55which is electrically connected to the metallic cylinder 5I. Thus it isseen that the voltage from the unidirectional voltage supply 31 isconnected between the cylinder 5I and rod 5|.

The triggering circuit 33 has two output terminals IBI and |62. Theterminal IBI is connected by a lead |63 to the terminal |24 and to aterminal IM on the saw-tooth voltage supply SIS. The terminal |32 isconnected by a lead |65 to the terminal |12 and to a terminal |61 on thesaw-tooth voltage supply 55.

Each of the electronic components 63, 64, 56, 61, and 63 are suppliedoperating voltage from a commercial source of power ITI).

Now consider the operation of the above-described apparatus and circuitswith a test material coated on the filament 35, the apparatus assembled,and the chamber I2 evacuated. Under these conditions the source of powerI1II i"s energized and the lament voltage supply E3 furtc the machinescrew'` onic equipment com- '4 nishes a heater voltage across thefilament 3'3. With the heating of the filament, ions of the testmaterial are formed in the region of the iilament age across the gapsbetween the tube sections.

Since the potential difference created along the tube sections 3|, 28,and 24 is positive in the region of the lament 33 and negative at thetube section 24, the positive ions of the test material formed by theheat of the filament 36 will be attracted away from the region of thefilament 35. It is well known that a charged particle will beaccelerated by an electric field and that the acceleration .isproportional to the product of the value of the electric eld and themass unit of the charged particle. The mass unit of the charged particleis the ratio of the charge to mass of the particle. From this it is seenthat ions having small mass will have short times of flight and thations of heavier mass will have longer times of iiight.

To counteract the defocusing tendency of the electric eld at the gapadjacent to the lament 35 because of the proximity of the lament 36, thescreen-type grids 39 and 4I are disposed across the adjacent openings ofthe two tube sections 3| and 23. Since the screen grid 39 covers theopening of the tube section 3|, a negative pulse of voltage from thetriggering circuit 68 is applied between the screen grid 33 and theiilament 35 at a predetermined interval to withdraw the ions from theregion of the filament 36 in a beam and to project them into theaccelerating force of the electric eld present at the following gap.Thus the ions are accelerated through the tube sections 28 toward thegrid structure 44 in the tube 42.

The triggering circuit 68 which applies a trigger pulse between thefilament 36 and grid 39 and extracts ions from the filament also appliesthe same trigger pulse to the saw-tooth voltage supply 36. The triggerpulse is delayed for a predetermined time within the saw-tooth voltagesupply 66 and initiates a saw-tooth pulse at a time when the lightestions from the filament 36 are arriving at the grid 44. The saw-toothpulse is applied between the grids 44 and 41, thus the light ions whicharrive at the grid 44 when the saw-tooth voltage is near zero areaccelerated very little. These light ions then enter the space betweenthe cylinder 5I and rod 6I. The light ions, having a relatively lowenergy are deected sharply by the unidirectional voltage 61 appliedbetween the cylinder 5| and rod 5|, The relatively light ions thusstrike the film 58 in a circumferential band near the entrance end ofthe cylinder 5I and irradiates a band on the film. The heavier ionsarrive at the grid 44 later than the light ions and therefore at a timewhen the saw-tooth voltage between the grids 44 and 41 is higher. Theheavier ions thus have a higher energy imparted to them by the saw-toothvoltage than do the light ions. The heavier ions so energized enter thespace between the cylinder 5| and rod 3| and are gradually deflected bythe unidirectional voltage therebetween unt-il they strike the film 53in a circumferential band near the closed end of the cylinder 5I. Thusit is seen that ions are separated according to their respective masses,and the relative amount of each io-n present is determined by the degreeof exposure of the corresponding bands on the film.

In the presently described embodiment of the invention the cylinder hasa diameter substantially twice that of the rod 6| has a diametersubstantially 0.1 the diameter of the cylinder 5| and the length of thecylinder is substantially twice its diameter. With these dimensions ithas been a simple matter to separate as many as ten ions of Successivemass numbers for a given set of operating voltages and conditions. It isreadily apparent that many of the parameters involved may be adjusted toshift the range of masses of ions detectable or to extend the rangethereof.

If it is desirable to collect ions as well as to separate ions ofdifferent masses it is possible to utilize a cylinder 5i havingcircumferential slits therein instead of a hlm. 'Ion collecting chamberswould then be disposed outside of the cylinder 5l communicating with theslits.

As well as being useful for micro-chemistry work, the present inventionis useful in the petroleum industry and in the control of some chemicaland manufacturing processes.

It is to be noted that the filament 36 may be replaced with numeroustypes of ion generators which readily adapt themselves to ionizingcontinuously-changing test materials. Nor is it desired to limit thetype of material which may be tested to solids which can be coated onthe iilament, for it is apparent that the filament 35 can be replacedwith apparatus for ionizing a vapor or gas.

While the salient features of this invention have been described indetail with respect to one embodiment, it will, of course, be apparentthat numerous modiiications may be made within the spirit and scope ofthe present invention and it is therefore not desired to limit theinvention to the exact details shown except insofar as they may bedefined in the following claims.

What is claimed is:

1. An isotope separator for determining the mass units of a testmaterial comprising an evacuated chamber, means for ionizing said testmaterial, electric field means for linearly accelerating said ionsthrough said chamber in accordance' with their mass units, a pair ofaccelerating grids disposed in the path of said ions, means connectedbetween said grids for impressing linearly varying voltage, anelectrostatic deflecting chamber disposed in the path of said ionsbeyond said accelerating grids, and means for collecting said ionswithin said defiection chamber.

2. An isotope separator for determining the mass units of a testmaterial comprising an evacuated chamber, a plurality of linearlydisposed tube sections within said chamber, means for ionizing said testmaterial disposed at one end of said tube sections, electrical means forestablishing accelerating electric fields between said tube sectionswhereby said ions are accelerated and linearly separated in accordancewith their mass units, a pair of accelerating grids disposedtransversely in the path of said ions in spaced-apart relation,accelerating voltage means applied between said accelerating grids, anelectrostatic ion deflector disposed adjacent said grids and parallel tothe path of said ions for the lateral deflection of said ions, and meansfor determining the disposition of said ions in said electrostatic iondefiector.

3. An isotope separator for determining the cylindrical tube 52; the

mass units of a test material comprising an evacuated chamber, aplurality of linearly disposed tube sections within said chamber, meansfor ionizing said test material at one end of said tube sections,resistance means connected between said tube sections, electrical meansconnected across said linearly disposed tube sections for establishingaccelerating electric fields between said tube sections, ionaccelerating grids disposed at the other end of said tube sections, anelectrostatic deflection chamber disposed in the ion path beyond saidaccelerating grids whereby said ions are deflected radially outward fromtheir normal paths, and ion collecting means disposed in the path of thedeflected ions.

4. An isotope separator for separating a test material according to itsmass units comprising an evacuated chamber, means for ionizing said testmaterial, electric field means for linearly accelerating said ionsthrough said chamber for linearly separating said ions according totheir mass units, accelerating grids disposed in the path of said ions,a saw-tooth accelerating voltage applied between said accelerating gridswhereby ions are accelerated according to the voltage existing betweensaid accelerating grids at their time of arrival thereat, an axialelectrode disposed in the path of said ions beyond said acceleratinggrids, a closed cylindrical electrode disposed coaxially about saidaxial electrode, a unidirectional voltage applied between said axialelectrode and said cylindrical electrode, and a photographic film axedto the interior surface of said cylindrical electrode.

5. A isotope separator for separating ions according to their mass unitscomprising a time-offiight mass spectrograph for linearly bunching.

ions according to their mass units, accelerating means disposed in thepath of said ions, whereby said ions are forwardly accelerated accordingto their time of arrival at said accelerating means, electrostatic meansfor radially deflecting said ions from the ion path, and ion collectionmeans disposed in the path of the defiected ions.

'6. An isotope separator for separating ions according to their massunits comprising a time-ofight mass spectrograph for linearly bunchingions according to their mass units, accelerating grids disposed in thepath of said ions, a sawtooth accelerating voltage applied between saidaccelerating grids whereby ions are accelerated according to the voltageexisting between said accelerating grids at their time of arrivalthereat, an axial electrode disposed in the path of said ions beyondsaid accelerating grids, a cylindrical electrode enclosing said axialelectrode and coaxial therewith, a unidirectional voltage appliedbetween said axial electrode and said cylindrical electrode, and iondetecting means afiixed to the interior surface of said cylindricalelectrode.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,582,216 Koppius Jan. 15, 1952 2,642,535 Schroeder June 16,1953 OTHER REFERENCES

